This application relates to the art of thermal switches and, more particularly, to thermal switches that use a contact member of temperature sensitive shape memory alloy for making and breaking a circuit. The thermal switch of the present invention is particularly applicable for use in batteries and will be described with specific reference thereto. However, it will be appreciated that the invention has broader aspects and can be used in other devices.
Shape memory alloys can be used to replace bimetals in thermal switches. A switch contact arm of shape memory alloy has a deformed shape at normal temperatures and changes to a recovered shape at elevated temperatures. These changes in shape of a shape memory alloy contact arm provide different contact arm positions that can be used to open and close an electrical circuit.
Electrical switch components of shape memory alloy have been incorporated in batteries to open the battery circuit when the battery overheats. It is difficult to incorporate a switch component of shape metal alloy into the battery construction in a manner that provides reliable operation and protects the shape memory alloy from the corrosive battery environment. Therefore, it would be desirable to have a self-contained unitary sealed thermal switch assembly that can be incorporated into batteries and other devices in a convenient and reliable manner.